Table 1.

The entry point and trajectory used in this study according to quantitative data measured by Rao et al. [20, 27]

Level	Entry point		Trajectory (degrees)
	Axial plane	Sagittal plane	Transverse angle	Sagittal angle
C3	The lateral margin of the lateral mass	4 mm from the inferior margin of the superior articular facet	45–50	According to C-arm oblique fluoroscopy
C4	One-fourth medial to the width of the lateral mass	3 mm from the inferior margin of the superior articular facet	45–50
C5	One-fourth medial to the width of the lateral mass	3 mm from the inferior margin of the superior articular facet	45
C6	One-fourth medial to the width of the lateral mass	2 mm from the inferior margin of the superior articular facet	40–45
C7	One-half of the width of the lateral mass	2 mm from the inferior margin of the superior articular facet	30–35